Antibiotic resistance and hypermutability of Escherichia coli O157 from feedlot cattle treated with growth-promoting agents.

摘要: In a longitudinal study (165 days), we investigated the effect of growth-promoting agents (monensin and trenbolone acetate-estradiol) an antibiotic (oxytetracycline) on incidence in feedlot steers Escherichia coli O157, including antibiotic-resistant hypermutable isolates. Eighty 16 pens were treated with eight combinations promoters, each treatment was duplicated. Fecal samples collected at nine different sampling times for detection E. O157. Overall, 50 O157 isolates detected animals, none found untreated animals. Compared controls, there significant association between utilization or antibiotics shedding day 137 (P = 0.03), when prevalence peak observed 50% detected. Multiplex PCR assays conducted some virulence genes. results indicated that all except one isolate possessed least Shiga toxin gene stx2. MICs 12 determined, oxytetracycline-resistant strains identified. Antibiotic-resistant considered distinct subpopulation by pulsed-field gel electrophoresis typing. Seven these isolated early (on before 25), among them two also as determined rifampin mutation frequencies. The proportion remained relatively constant throughout period. These indicate use beef production may increase risk environmental contamination